Leaders from 28 European and North American nations on Sunday signed off on a high-profile review of NATO’s overall deterrence posture that maintains nuclear weapons as a key means of deterrence against enemy threats.

The Deterrence and Defense Posture Review approved at the military alliance’s two-day summit in Chicago states that “nuclear weapons are a core component of NATO’s overall capabilities for deterrence and defense alongside conventional and missile defense forces. The review has shown that the alliance’s nuclear force posture currently meets the criteria for an effective deterrence and defense posture.”

NATO includes three nuclear powers – France, the United Kingdom, and the United States. London deploys its nuclear arms solely aboard ballistic missile submarines, while France uses both submarines and strategic bombers. The United States wields the full nuclear triad of land-based missiles, bombers, and submarines, including close to 200 nonstrategic weapons fielded in Europe.

The arsenals are intended to prevent aggression against their possessor states, and to provide a “nuclear umbrella” for partner nations in NATO and beyond.

Organizations pursuing global nuclear disarmament have called on NATO to draw back from the reliance on strategic weapons as a component of defense, which they see as an increasingly obsolete holdover from the Cold War.

At its previous summit in 2010, in Lisbon, Portugal, the 28-member alliance under a revised Strategic Concept committed itself for the first time “to the goal of creating the conditions for a world without nuclear weapons”.

However, the DDPR assessment, which was mandated by the Lisbon summit, reaffirmed that “the supreme guarantee of the allies is provided by the strategic nuclear forces of the alliance, particularly those of the United States. It noted that the strategic arsenals of France and the United Kingdom “contribute to the overall deterrence and security of the allies.”

The Western military bloc this weekend re-endorsed the goal of creating the right atmosphere for nuclear disarmament while maintaining that “as long as nuclear weapons exist, NATO will remain a nuclear alliance.”

Disarmament advocates were not particularly optimistic for significant headway on the issue at the Chicago summit. It was hoped, though, the alliance might take limited steps such as endorsing a change to the deterrence posture to declare that the central purpose of nuclear weapons was to discourage a similar attack.

Instead, alliance leaders endorsed the view in the DDPR document of “the importance of the independent and unilateral negative surety assurances offered by the United States, the United Kingdom and France.”

“It would not be appropriate for NATO to comment on the individual decisions of sovereign states” when it comes to negative security guarantees -- the pledge not to use nuclear weapons against states that do not possess such arms -- an alliance official said to Global Security Newswire in explaining why NATO did not issue a declaratory policy on the specific role of nuclear weapons. He requested anonymity under standard diplomatic protocol.

In its 2010 Nuclear Posture Review, Washington specified it would not use its nuclear weapons on non-nuclear states that adhere to international nonproliferation regimes. London offered a similar assurance that year in its Strategic Defense and Security Review. Only Paris has refused to specify it will not use its nuclear arsenal on countries without such a deterrent of their own, according to a March Arms Control Association analysis.

The new Deterrence and Defense Posture Review also did not take up a call by arms control advocates for the immediate reduction, withdrawal, or consolidation of the U.S. B-61 gravity bombs understood to be fielded in Belgium, Germany, Italy, the Netherlands, and Turkey.

Rather, the document commits the alliance to “create the conditions … for further reductions of nonstrategic nuclear weapons assigned to NATO” and to “ensure that all components of NATO’s nuclear deterrent remain safe, secure, and effective.”

The military rationale for the fielded U.S. tactical weapons is increasingly being called into question, more than two decades after the fall of the Soviet Union. The Obama administration has signaled its interest in withdrawing the gravity bombs under a new nuclear arms control treaty with Russia. While Germany and other nations have indicated support for withdrawal, not all NATO members are comfortable with the United States removing what they view as a key symbol of the enduring U.S. commitment to the physical security of Europe.

One looming problem for the alliance is the modernization schedules of the European nuclear-capable aircraft that would deliver the U.S. tactical weapons in the event of an ordered attack.

The attack-fighter planes of Belgium, Germany, Italy and the Netherlands are nearing the end of their shelf life. The four countries must decide within the next several years whether to order replacement fighter planes that can carry both nuclear and conventional bombs; Turkey is understood to no longer maintain aircraft that can deliver free-fall nuclear weapons.

Some observers had wanted NATO leaders to use the Chicago summit to discuss a schedule and process for determining the future of U.S. tactical weapons in Europe.

The DDPR document calls for “the appropriate committees to develop concepts for how to ensure the broadest possible participation of allies concerned in their nuclear sharing arrangements, including in case NATO were to decide to reduce its reliance on nonstrategic nuclear weapons based in Europe.” “Allies concerned” refers to all NATO countries but France, which does not participate in the Nuclear Planning Group.

The alliance did specify its willingness to see the U.S. gravity bombs withdrawn “in the context of reciprocal steps by Russia, taking into account the greater Russian stockpiles of nonstrategic nuclear weapons stationed in the Euro-Atlantic area.”

Russia is estimated to retain some 2,000 tactical nuclear warheads "in central storage" and another 5,500 bombs that are no longer in active service and are awaiting potential disassembly.

“NATO will now have an operationally meaningful ballistic missile defense mission. It will be limited in the initial phase, but it will expand over time,” U.S. Ambassador to NATO Ivo Daalder said at a Sunday evening press briefing. “It will, as of today, provide real protection for parts of NATO Europe against ballistic missile attack.”

The antimissile capability involves a U.S. long-range radar unit fielded in Turkey, rotating U.S. Aegis-equipped guided missile destroyers in the Mediterranean and a command-and-control center based in Ramstein, Germany.

“With initial NATO command and control procedures in place, the [U.S.] president has directed the U.S. [secretary of Defense] to transfer operational control of the U.S. radar in Turkey to NATO,” states a White House fact sheet. “The radar’s information, combined with the NATO command-and-control system, gives NATO missile defense commanders a comprehensive and real-time operational picture, enabling them to employ the available missile defense assets effectively.”

The designated U.S. Aegis-equipped destroyers in Europe can also be assigned to NATO’s operational control “as necessary,” according to the fact sheet.

“We designated the supreme allied commander of Europe, Adm. Jim Stavridis, as the commander for the ballistic defense mission. We have tested and validated the command-and-control capability by all 28 allies,” Daalder said. “Allies themselves have committed to invest over $1 billion in command-and-control and communications infrastructure needed to support the NATO ballistic missile defense system.”

At another Sunday press conference, NATO Secretary General Anders Fogh Rasmussen described the achievement as “the first step towards our long-term goal of providing full coverage and protection for all NATO European populations, territory and forces.”

With the United States taking the lead and shouldering the large majority of the costs, alliance members intend to enhance and coordinate their respective antimissile capabilities under NATO command-and-control. The Obama administration’s “phased adaptive approach” lies at the heart of this endeavor; it calls for the gradual fielding between now and 2020 of increasingly advanced sea- and land-based interceptors around Europe.

The interim missile shield announced on Sunday is to be followed in three years with a declaration of an “initial operational” antimissile capacity and finally in 2018 with the achievement of a “full operational” capability, the fact sheet says.

“This is true trans-Atlantic teamwork: the United States and European allies investing in our common security,” Rasmussen said. “It is an excellent example of the renewed culture of cooperation which we call Smart Defense: countries working together to develop capabilities which they could not develop alone.”

Russia has been a vehement critic of the NATO plan, which it suspects of being aimed at countering the nation’s strategic nuclear forces. Brussels and Washington say the system is aimed instead at Iran, but have dismissed Moscow’s demand for a legally binding pledge on the targeting issue. Russia, in turn, has threatened a military response including deployment of short-range ballistic missiles in territory bordering NATO states Poland and Lithuania.

“We have invited Russia to cooperate on missile defense and this invitation still stands,” Rasmussen said.